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Catherine W Morgans, Gaoying Ren, Tammie Haley, Weihong Xiong, Maria Borisovska, Cyrus McHugh, Margaret Veruki, Robert M Duvoisin; Expression of Kv11.1 in retinal ON-bipolar cells.. Invest. Ophthalmol. Vis. Sci. 2017;58(8):2229.
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© ARVO (1962-2015); The Authors (2016-present)
This study aims to determine if ON-bipolar cell responses to light are influenced by dendritic potassium channels. We focused on the Kv11.1 (erg1, hERG) channel as it has been shown previously to be expressed in bipolar cells.
Kv11.1 antibodies were validated by immunofluorescence and western blotting using Kv11.1-transfected HEK293 cells. Kv11.1 expression in mouse retina was confirmed by western blotting, and its distribution in the retina determined by immunofluorescence confocal microscopy. The physiological role of Kv11.1 in bipolar cells was assessed by measuring the effect of the Kv11.1 blocker, E-4031, on electroretinogram (ERG) recordings and patch-clamp recordings of bipolar cells.
Two validated antibodies against different epitopes of Kv11.1 revealed immunofluorescent labeling of the inner and outer plexiform layers (IPL and OPL) of the mouse retina. Western blots of retinal proteins revealed a band of approximately 150 kD with both antibodies, consistent with expression of KV11.1 isoform a (ERG1a). In the OPL, Kv11.1 co-localized with TRPM1 and GPR179 in the dendritic tips of ON-bipolar cells, and occasionally with TRPM1 in ON-bipolar cell bodies. Kv11.1 immunofluorescence was unchanged in TRPM1 knockout and PKCα knockout retina. Patch-clamp recordings from rod bipolar cells in retinal slices revealed an E-4031 sensitive potassium current. The putative Kv11.1 current was present in both intact cells and cells where the axon terminal was severed, indicating that the current is likely to arise from the dendrites. Injection of E-4031 (Kv11.1 blocker) into one eye caused a delay and decrease in amplitude of the b-wave of the ERG compared to the contralateral eye that was injected with PBS only. The effect of E-4031 on the ERG was absent in ERGs from PKCα knockout mice.
Kv11.1 is expressed in retinal ON-bipolar cells, where it is localized to the dendrites. ERG recordings in the presence and absence of E-4031 indicate a role for Kv11.1 in shaping the light reponse of ON-bipolar cells. The lack of effect of E-4031 on ERGs from PKCα knockout mice suggests that Kv11.1 activity may be regulated by phosphorylation by PKCα.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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